I think part of your problem is that you think this is an EXACT science. But, it's not. There are no magic chemical levels, where at pH 7.3421 exactly, the calcium starts to precipitate, or at FC=15.03ppm the algae will start to die.

Pool chemistry is approximate, not exact! There are no 'perfect' levels; there's only 'good enough', or 'not good enough' . . . and where those levels are varies from pool to pool.

So, for example, you need to think of your pool as "27,000 gallons" (or more likely, 26,000 -- values by liner companies and builders are almost always inflated!), NOT 26,696 gallons.

Here's a general chemical rule that will help you avoid problems: "When treating your pool, if you are unsure, over-dose with chlorine but under-dose with everything else!"